Hi,
Planning a trip from Denver to Durango and back . While going, planning on going through Alamosa for a night and then onto Durango for 3 days.

While coming back, I thought of driving back from Durango and stopping at Black Canyon South rim ( just brief stops ) and then onto Estes Park.
Is that drive too much for one day if I leave early - say 7:30- 8AM ?
I'd like to avoid night driving if possible.

According to Google maps it will take 8.5 hours to do the drive, not counting the various stops. Up to you if you really want to spend such a long day on the road.

When???? It is a long mountain drive. The roads are good but no four lanes. And I have found Google maps to be optimistic for travel times in the mountains. And, if there is a tendency to do any sightseeing then it will be a ten or eleven hour trip. Are you planning to Estes Park from the west or southeast?

Thank you, this would be the last week of August.

Google maps gave me a route of via US-550 N, US-550 and US-50 E and so entering Estes Park through 36 West.

Looks like too much in a day. Maybe it is better to stop at Montrose on the way back.
Some research tells me that is a good stop over for Black Canyon.. thoughts?

Montrose is the closest town to Black Canyon and is probably the best place for a stop. You could see the Black Canyon in the late afternoon/early evening and then backtrack the few miles to Montrose for the night.

I would keep going to Gunnison. No point in back tracking to Montrose since it is in the wrong direction. Or even as far as Salida depending on your timing. Last week of August will still give sunlight to about 7.45.